Engines may increase output power by using boosting devices that compress intake air. Since charge compression increases air temperature, charge air coolers may be utilized downstream of a compressor to cool the compressed air, further increasing the potential power output of the engine. Ambient air from outside the vehicle is delivered across the charge air cooler to cool intake air passing through the inside of the charge air cooler. Condensate may form in the charge air cooler when the ambient air temperature decreases, or during humid or rainy weather conditions, where the intake air is cooled below the water dew point. Condensate may collect at the bottom of the charge air cooler, or in the internal passages, and cooling turbulators. When torque is increased, such as during acceleration, increased mass airflow may strip the condensate from the charge air cooler, drawing it into the engine and increasing the likelihood of engine misfire.
One example approach to prevent engine misfire due to condensate ingestion includes trapping and/or draining the condensate from the charge air cooler. While this may reduce condensate levels in the CAC, condensate is moved to an alternate location or reservoir, which may be subject to other condensate problems such as freezing and corrosion.
Another example approach for addressing moisture induced misfires is shown by Glugla et al. in US 20140109568. Therein, by increasing airflow through the charge air cooler, controlled amounts of condensate is blown off into the engine. However, the inventors herein have identified potential issues with such an approach. As one example, engine combustion stability may be sensitive to the amount of condensate. Consequently, even small errors in condensate metering can lead to misfires. Further, increasing airflow through the charge air cooler causes increased airflow to the engine. In order to compensate for increased torque due to the increased airflow, a vehicle controller may adjust one or more engine actuators (e.g., retard spark timing from MBT) to reduce torque. Such measures for torque compensation may degrade the engine efficiency.
In yet another example approach shown by Glugla in U.S. Pat. No. 8,961,368, misfires due to ingestion of condensate is addressed by purging condensate into the engine during a deceleration event when cylinder combustion is not occurring. This may increase deposition of condensate within the engine cylinders, which leads to rust formation and hence, cause structural damage to engine parts. Further, purging condensate into the engine when the cylinders are not combusting may cause the condensate to deposit within the catalytic converter in the exhaust passage. This may lead to degradation of the exhaust catalyst.
Taken together, even with controlled purging or purging when cylinders are not combusting, purging condensate from the charge air cooler into the engine may increase deposition of the condensate within the engine and the exhaust as the condensate travels through the engine and the exhaust parts. As a result, in addition to structural damage caused by condensate deposition, during purging or subsequent engine combustion after purging, misfires due to condensate ingestion are also increased. Further, due to increased airflow to the engine and the torque compensation approaches to counteract the excess torque from the increased airflow, engine efficiency is reduced.
In one example, some of the above issues may be addressed by a method for a boosted engine, comprising: responsive to a condensate level within a charge air cooler increasing above a threshold, reverse rotating the engine unfueled and flowing pressurized air from an intake manifold of the engine towards an intake air filter via the charge air cooler. In this way, condensate may be purged away from the engine, thereby reducing condensate deposition within the engine and the likelihood of misfires.
As an example, during selected vehicle operating conditions, such as during key OFF conditions or responsive to a key ON event, a vehicle controller may utilize an onboard DC motor to rotate the engine in a reverse direction unfueled to generate pressure inside the intake manifold. The pressurized air in the intake manifold is flown towards the intake air filter via the charge air cooler. As a result, condensate within the charge air cooler is purged away from the engine and towards the intake air filter. The purged condensate may then be delivered to the atmosphere via a conduit parallel to the intake air filter and including a check valve so that condensate does not deposit within the air filter, thus reducing the formation of molds within the air filter. In this way, by purging condensate from the charge air cooler towards the intake air filter, condensate deposition within the engine cylinders and the exhaust system is reduced. Consequently, misfires due to condensate ingestion are reduced. Further, structural damage to engine parts and the exhaust catalyst due to rust formation resulting from condensate deposition is reduced. Further still, by purging from the charge air cooler towards the intake air filter, a shorter path is provided for the condensate to travel from the charge air cooler to the atmosphere, thus further reducing the chances of condensate deposition within the engine system during purging. Further, by performing the purge operation during key OFF and when the engine is not utilized to propel the vehicle, torque compensation measures, such as spark retard that may be required when purging by increasing airflow through the engine, may not be utilized.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.